Rivers of Fire: Red Planet Channels Likely Formed by Lava

What scientists have interpreted as ancient riverbeds, are more likely to be lava
flows.

The severe volcanic activity that created the largest outflow channels might have
hampered the planet’s ability to support complex organisms living on the surface.

Since the Mars Viking missions of the ’70s, humans have compared the topography of the Red Planet’s surface to their
home and imagined a world that once contained flowing rivers that carved channels
and canyons.

But David Leverington, an associate professor in the Department of Geosciences at
Texas Tech, said what we interpret as the largest ancient riverbeds on Mars most likely
were created not by water, but by massive, fast-moving, low-viscosity lava flows that
ravaged the planet’s surface in a way we don’t see on Earth.

He said most Mars researchers believe these channels were created by water, and that
has buoyed the belief that life on the planet may be or once was possible. But the
water theory has several holes in it.

In his recent study in Geomorphology, which will publish in September 2011, Leverington uses recent high-resolution photographs
and mineralogical data to help lay out his theory for why lava is a much more likely
culprit for creating the largest class of the outflow channels and canyons, which
can stretch up to 1,800 miles. Read the article here.

Leverington said what we interpret as the largest ancient riverbeds on Mars most likely
were created not by water, but by massive, fast-moving, low-viscosity lava flows.

“This paper highlights the strengths and weaknesses of the two theories that these
outflow channels were formed by volcanic or water activity,” he said. “Many scientists
realize there are issues with aqueous interpretations of these channels. They recognize
that if these systems formed by giant subsurface flows of water, there would need
to have been extraordinarily high ground permeability, up to a million or more times
greater than what we’d expect for the crust of the Earth, just to allow sufficient
amounts of water to make it to the outflow locations and erupt to the surface.”

Channels Formed by Lava, Not Water

While water exists on the planet, most of it appears to be trapped at the poles and
at higher latitudes in the form of ice, Leverington said. Most modern theories on
the creation of the largest channel systems center on the action of surface floodwaters
forced up from enormous aquifers.

Martian water does exist in large quantities, Leverington said, but nowhere near the
volume that we have on Earth.

“What we know about Mars’ water is that it’s primarily in the solid state and concentrated
at higher latitudes,” he said. “We see large concentrations at the polar icecaps.
Various measurements also have been made to infer the presence of water at high latitudes
to mid latitudes where there appears to be ice frozen below the surface. An important
question has recently arisen: Is there much more water on Mars than this? While there
is a considerable volume of water on Mars, it may not be sufficient to have driven
the kinds of channel-forming processes many believe happened.”

The Martian outflow channels superficially resemble channels on Earth that formed
by floods from giant glacial lakes. However, unlike Earth’s water-formed channels,
Leverington said the large Martian canyons do not feature obvious river deposits and
don’t terminate in delta-like, sediment-laden mouths, such as at the end of the Mississippi
River. Instead, they fade into vast plains composed of volcanic basalt.

“We see abundant evidence for past eruptions of lava at the heads of these large systems,
for flows along these systems and for extraordinarily large volumes of lava at the
mouths of these systems,” he said. “These characteristics are very similar to what
we see at volcanic channels on the moon and on Venus. There’s really no known process
for the rapid eruption of large amounts of water from aquifers to form channels that
are thousands of miles long. We do have evidence of this happening through past volcanic
processes on the moon and Venus.”

These kinds of channel-forming volcanic flows wouldn’t have been like anything ever
seen by humans on Earth, Leverington said, though evidence suggests these types of
massive lava flows could have occurred very early in our planet’s history.

Images of Mars' Volcanic Channels

[nggallery id=101]

Water and Life on Mars

Though clays and other minerals indicate there would have been water at least in the
vapor form during Mars’ early history, other ancient minerals that should have been
affected by the later presence of water are mostly in their natural and relatively
unaltered state. Many of these pristine minerals are found in the valleys and terminal
basins of the largest Martian channels

“If we look at modern mineralogy of ancient materials exposed on the surface of Mars,
we see some evidence that water was present in the vapor or liquid state very early
on,” Leverington said. “We also know of many materials that should have been altered
by wet conditions quite readily that haven’t been greatly altered, though they have
been exposed since quite early in Mars’ history. Some ancient exposed bedrock contains
large amounts of iron-rich olivine, and that has not been altered in the past 3.5
billion years. That would suggest that most of Mars history has been extraordinarily
dry.

“Surface conditions were likely to have been relatively wet in large regions only
in Mars’ earliest development stages. These wet stages pre-date the development of
the large outflow channels on Mars.”

But that doesn’t mean that life on Mars couldn’t have developed, he said, though the
severe volcanic activity that created the largest outflow channels might have hampered
the planet’s ability to support complex organisms living on the surface.

“There’s still the potential for life to have developed and even flourished in the
earliest and wettest stages of Mars’ history,” Leverington said. “Simple life forms,
such as bacteria-like organisms, could have lingered in the subsurface under the dry
conditions that ultimately became widespread. But if the large outflow channels formed
through volcanic mechanisms rather than substantial water flow, that mainly restricts
the environments conducive to the development of life to the earliest stages of that
planet’s history.”

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The Moon and Venus

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